Have tried multiple cards that always work on websites and all cards declined with this error
Hmm... Error with Transaction
Unfortunately, the payment was not successful.
The error was: Your card was declined.

Hello Alex,
Thank you for your interest in upgrading! You will have to call your bank or login to your bank account and "approve" us as a vendor.
The first attempt resulted in an error, "Payment declined by the issuing bank."
The second was, "You previously attempted to charge this card. When the customer's bank declined that payment, it directed Stripe to block future attempts."
You can also pay by credit card by using the "PayPal" option, and then find the "proceed without PayPal account" link (or equivalent).
I hope this helps. Please let me know if I can help further.